1. Field of the Invention
The present invention relates generally to a position sensor and, more particularly, to a position sensor which utilizes two tracks arranged in a side-by-side configuration in which each track comprises a plurality of magnetic and nonmagnetic segments with a magnetically sensitive device disposed proximate to each track.
2. Description of the Prior Art
Many different devices are known to those skilled in the art for detecting the movement of an object relative to the position of a sensor. These devices can utilize photoelectric or magnetic sensors, among many other alternatives, to determine the position, speed and direction of motion of an object.
U.S. Pat. No. 4,853,632, which issued to Nagano et al on Aug. 1, 1989 describes an apparatus for magnetically detecting a position of a moveable magnetic body. It includes a magnetic field intensity sensing structure formed by a pair of magneto resistors. The magnetic field intensity sensing structure is disposed opposite to a magnetic body arranged for movement relative thereto in a magnetic field. It generates a first electrical signal of sinusoidal waveform in response to a change in the intensity of the magnetic field due to the relative movement of the magnetic body. This first electrical signal appears from the apparatus as a second electrical signal of rectangular waveform or sinusoidal waveform having am amplified magnitude.
U.S. Pat. No. 4,970,463, which issued to Wolf et al on Nov. 13, 1990, describes a temperature stable proximity sensor. The ferrous object sensor assembly is capable of sensing the presence or absence of an object of high magnetic permeability, such as a tooth or notch on a rotatable mounted ferrous wheel, at zero speed and immediately upon power-up. The assembly comprises a permanent magnet and a magnetic flux responsive sensor having a sensing plane which produces an electrical output signal which varies as a function of the change of magnetic flux density. The sensor assembly does not rely upon pole face magnetism as some known conventional sensors do but, rather, relies upon the radial component of magnetic flux density emanating from a lateral surface of the magnet intermediate opposing pole faces.
U.S. Pat. No. 5,018,384, which issued to Hayashi et al on May 28, 1991, discloses a rotational speed detector which is incorporated in an antiskid brake system for an automobile. It detects a rotational speed of a wheel. The sensor assembly is provided on either one of the outer and inner rings of a wheel and is biased toward a sensor rotor that is provided on the other of the two rings in such a manner that the sensor assembly is slidable on the sensor rotor. This maintains the distance between the rotational speed sensor assembly and the sensor rotor at a constant level.
U.S. Pat. No. 5,070,727, which issued to Davis et al on Dec. 10, 1991, describes a crank shaft angular position detecting apparatus. The apparatus is used for detecting the angular position of the crank shaft of an internal combustion engine. The crank shaft drives a timing wheel which has a plurality of circumferentially spaced slots located along its outer periphery. Two angularly spaced sensors are located adjacent the slots. The sensors develop voltage pulses as the slits move past the sensors. Two phase displaced pulse trains are developed, one by each sensor, as the wheel rotates. The pattern of slots and the angular spacing of the sensors is such that a varying number of pulses of one pulse train occurs between consecutive occurring pulses of the other pulse train. The varying number of pulses provide different patterns and each pattern in indicative of a crank shaft position.
U.S. Pat. No. 5,086,272, which issued to Henrichsen on Feb. 4, 1992, describes an apparatus for distinguishing between opposed directions of relative motion of a part having magnetic variations. The device contains an inductive magnetic sensor disposed adjacent to the path of motion of the magnetic variations. It has portions with different magnetic couplings with the magnetic variations spaced in the direction of motion of the part.
U.S. Pat. No. 5,111,138, which issued to Kramer on May 5, 1992, describes a speed sensor which has a closed magnetic flux path for sensing speed from an axial space of a rotating member. The sensor utilizes a stator which includes two circumferentially spaced elements which are interconnected by a low magnetic permeability member. The elements have alternating regions which provide a variation in magnetic permeability. A rotor which is arranged for rotation about a rotational axis includes alternating regions of magnetic permeability which interact with the stator. A magnet is located between the elements of the stator and the structural interconnection therebetween. A coil of wire is placed around the structural interconnecting member to sense variations in magnetic field which are caused by the change in reluctance as the respective regions of magnetic permeability of the elements and rotor pass one another.
In position sensing devices which utilize magnetically sensitive devices, such as Hall elements, and rely on changing magnetic field intensities affected by the movement of magnetic material proximate the sensor exhibit certain limitations in particular applications. For example, when a plurality of teeth and interstitial spaces are used as part of the moveable object, the magnetic effect sensed by the magnetically sensitive device can vary significantly as a function of the width of the tooth or slot adjacent to it. In other words, narrow slots cause different magnetic field deviations than wide slots and narrow teeth cause different magnetic field variations than wide teeth. As will be described in greater detail below, these different effects caused by wide and narrow teeth or slots increase the difficulty in using sensors of this type. These problems are exacerbated in circumstances where a large number of teeth and slots are required when the diameter of the moveable object is relatively small. In situations of this type, it is necessary to space the teeth and slots closely together. It would therefore be highly beneficial to the technology of position sensing if a sensing system could distinguish narrow slots from wide slots and narrow teeth from wide teeth with a high degree of confidence and without requiring a large angular movement of the moveable object before being able to determine the position of the object.